A conventional clamping device of stringing machine is shown in FIG. 1 and generally includes a body 1, a tapered member 2, a base 3, a knob 4 and a slide block 5. The body 1 has a tapered hole 101, a recess 102 and a tube 103 which extends upward from the body 1. The tapered member 2 is engaged with the tapered hole 101 and a protrusion 201 and a stop block 202 are fixed to an underside of the tapered member 2 so as to be connected to the rail of the stringing machine. The tube 103 receives the clamping device which is not shown. The base 3 is engaged with the recess 102 and includes a shaft 301 which has an eccentric section 302. A notch 303 is defined in the base 3 and located corresponding to the notch 303. The knob 4 is connected to a top of the shaft 301. A slot 104 is defined between the tapered hole 101 and the recess 102 so that the slide block 5 is engaged with the slot 104. The slide block 5 has a bolt 501 at an end thereof and the bolt 501 faces the recess 102 so as to be in contact with the eccentric section 302 of the shaft 301. A cap 502 is mounted to the contact surface between the bolt 501 and the eccentric section 302. The slide block 5 has an inclined surface 503 which is in contact with tapered member 2 and matches with the tapered member 2.
When positioning the body 1 to prevent the clamping device from shifting, the knob 4 is rotated so that the eccentric section 302 pushes the bolt 501 and the slide block 5 moves horizontally such that the tapered member 2 is pushed upward by the inclined surface 503. The stop block 202 is in contact with the rail 9 so that the body 1 is positioned and does not rotate. When the body 1 is to be released from the position, the knob 4 is rotated in opposite direction and the torsion spring 401 in the knob 4 rotates the knob 4 at high speed and back to its original position. The eccentric section 302 of the shaft 301 is no in contact with the bolt 501 so that the stop block 202 is disengaged form the rail 9. The tapered member 2 is lowered due to the gravity and the body 1 is freely rotated and moved along the rail 9.
It is noted that when the knob 4 is rotated to secure the body 1, during the stringing processes, the knob 4 might be rotated unintentionally by the user. Because the clamping device does not have a positioning feature, the knob 4 is easily rotated in opposite direction by the torsion spring 401. This shortcoming makes stringing machine to be un-reliable.
The present invention intends to provide a clamping device which improves the shortcoming mentioned above so that the stringing machine is more reliable.